Vascular prosthesis

ABSTRACT

Luminal prostheses comprise adjacent expansible segments, typically serpentine ring segments joined by sigmoidal links. By properly orienting the sigmoidal links and aligning hinge regions on adjacent serpentine rings, enhanced performance can be obtained.

BACKGROUND OF THE INVENTION

The present invention relates generally to medical devices and methodsusing the same. More particularly, the present invention relates to thestructure of radially expansible luminal prostheses, including stentsand grafts.

Luminal prostheses are provided for a variety of medical purposes. Forexample, luminal stents can be placed in various body lumens, such asblood vessels, the ureter, the urethra, biliary tract, andgastrointestinal tract, for maintaining patency. Luminal stents areparticularly useful for placement in pre-dilated atherosclerotic sitesin blood vessels. Luminal grafts can be placed in blood vessels toprovide support in diseased regions, such as aortic abdominal, and otheraneurysms.

Both stent and graft prostheses must meet certain mechanical criteria tofunction successfully. In particular, such prostheses should be at leastpartly flexible or articulated (such as rigid sections that articulaterelative to one another) over their lengths so that they may be advancedthrough tortuous body lumens, such as those of the coronary vasculature.In addition, the prostheses should preferably maintain their originallength or foreshorten minimally when the prostheses assume an expandedconfiguration. Further such prostheses must have sufficient mechanicalstrength, particularly hoop strength, in order to mechanically augmentthe luminal wall strength and thus assure lumen patency. The ability tomeet these requirements is severely limited in the case of cylindricalendoluminal prostheses which are delivered in a radially constrained orcollapsed configuration. Such prostheses must radially expand at atarget site within the body lumen, so any adaptations which are intendedto enhance flexibility will not interfere with the ability to radiallyexpand or to maintain strength once expanded.

Such prostheses, including stents, can suffer from a variety ofperformance limitations including fishscaling, poor tracking, flaring,and unwanted twisting upon deployment. Fishscaling is a phenomena whichoccurs when the prosthesis is flexed or articulated during delivery ortracking, resulting in the expanded prosthesis having unwanted outwardprotrusion of portions of the prosthesis from its surface, therebyincreasing the likelihood that the prosthesis will dig into or otherwiseengage the wall of the body lumen during delivery and even arrest theprogress of the prosthesis and its delivery system to the diseasedregion (or target site). Poor tracking performance may be exhibited whenthe prosthesis' ability to pass smoothly through tortuous pathways isbelow the desired level. Flaring is a phenomena which occurs when thedistal or proximal end of the prosthesis are bent outward, assuming acrown-like configuration due to bending forces placed on these elementsas the prosthesis passes through tortuous body passageways, oftenresulting in the same deleterious effects as the previously describedfishscaling phenomenon, injuring or traumatizing the blood vessel wallas the prosthesis is delivered or tracked within the blood vessel. Acommon problem with many of the current devices is their being twistedupon or after deployment in the lumen, resulting in unwanteddeformation. The unwanted twisting may occur during the deployment ofthe device. Often, the devices, when for example deployed by anexpandable member such as a balloon, is first expanded at its two endswith the midsection, usually at the center, of the device exhibiting aninward crease with its peak pointing inward in the luminal direction.Such inwardly facing peaks then result in a smaller local inner diameterof the device, leading to obstruction of the lumen.

Accordingly, it would be a significant advance to provide improveddevices and methods using the same. This invention satisfies at leastsome of these and other needs.

BRIEF SUMMARY OF THE INVENTION

The present invention provides improved luminal prostheses suitable forendoluminal placement within body lumens, particularly blood vessels,and most particularly coronary and peripheral arteries. The luminalprostheses may be in the form of stents, intended for maintainingluminal patency, or may be in the form of grafts, intended forprotecting or enhancing the strength of a luminal wall. Generally, theterm “stent” will be used to denote a vascular or other scaffoldstructure comprising expansible components, such as ring segments, whichwhen expanded form an open lattice or framework which is disposedagainst the luminal wall. In contrast, the term “graft” will generallydenote such as luminal scaffold which is covered by a liner, membrane,or other permeable or impermeable layer which covers at least a portionof the scaffold. The drawings included herein are generally directed atstent structures, but it will be appreciated that corresponding graftstructures could be provided by incorporating a liner, membrane, or thelike, on either the outer or inner surfaces of the stent.

The prostheses are preferably placed endoluminally. As used herein,“endoluminally” will mean placement through a body opening or bypercutaneous or cutdown procedures, wherein the prosthesis istransluminally advanced through the body lumen from a remote location toa target site in the lumen. In vascular procedures, the prostheses willtypically be introduced “endovascularly” using a catheter over aguidewire under fluoroscopic guidance. The catheters and guidewires maybe introduced through conventional access sites to the vascular system,such as through the femoral artery, or brachial, subclavian or radialarteries, for access to the coronary arteries.

A luminal prosthesis according to the present invention will usuallycomprise at least two radially expansible, usually cylindrical, ringsegments. Typically, the prostheses will have at least four, and oftenfive, six, seven, eight, ten, or more ring segments. At least some ofthe ring segments will be adjacent to each other but others may beseparated by other non-ring structures.

The luminal prostheses of the present invention are radially expansible.“Radially expansible” as used here in, refers to a prosthesis that canbe converted from a small diameter configuration (used for endoluminalplacement) to a radially expanded, usually cylindrical, configurationwhich is achieved when the prosthesis is implanted at the desired targetsite.

The prosthesis may be minimally resilient, e.g., malleable, thusrequiring the application of an internal force to expand and set it atthe target site. Typically, the expansive force can be provided by aballoon, such as the balloon of an angioplasty catheter for vascularprocedures.

In an embodiment, usually by the application of a radially outwardinternal force to expand a minimally resilient (usually malleable)prosthesis structure. Such radially outward internal force will usuallybe provided by an inflatable balloon, and such balloon expansible stentsare well-known in the art and described in the background referenceswhich have been cited above and are incorporated herein by reference.

Alternatively, at least some of the radially expansible luminalprostheses of the present invention may be self-expanding. Byfabricating the prostheses from a resilient material, usually a metal,such as spring stainless steel, a nickel-titanium alloy (such asNitinol® alloy), or the like, the prosthesis can be designed to have alarge (fully expanded) diameter in an unconstrained state. The diameterof the prosthesis can be reduced by applying a radial constraint, e.g.,by placing the prosthesis within a sleeve, tube, or other constrainingstructure. In that way, the self-expanding prosthesis can be deliveredwhile constrained and deployed by releasing the constraint at the targetsite within the body lumen. The general principles of constructingself-expanding stents and other luminal prostheses are also well-knownin the art and described in at least some of the background referenceswhich have previously been incorporated herein.

In an embodiment, a radially expansible luminal prosthesis comprises aplurality of unit segments, usually serpentine ring segments, includingstruts regions connected by hinge regions.

In an embodiment, the hinge regions are usually formed by a shortcurved, normally a C- or U-shaped region which permits the connectedstruts to reverse direction in order to define the serpentine ringpattern. In an embodiment, the hinge region includes an apex portionwith side potions extending on either side of the apex, the sideportions transforming into the strut region of the ring.

In an embodiment at least some, usually all of the hinge regions areradially off set from one another. In another embodiment, at least some,usually all of the hinge regions are radially aligned with one another.

At least some of the longitudinally adjacent serpentine rings are joinedby links which may be malleable or elastically deformable in order toallow the adjacent segments to flex relative to each other duringprosthesis delivery and expansion.

The links connect at least some of the hinge regions of one ring to atleast some of the hinge regions of another ring which is longitudinallyoffset and adjacent to the one ring. In an embodiment, the connectedring segments are longitudinally immediately adjacent one another, withthe connecting links forming a tubular column comprising a plurality oflinks which are radially offset from one another.

The links can extend from any portion of the hinge region, such as theapex or the side portions, or somewhere in between. In an embodiment, atleast some, preferably all, of the links extend laterally from eachhinge region, typically from a point where the hinge region transformsinto the strut.

In an embodiment, the links generally have a smooth, multi (usuallydouble) curvature shape, usually in a sigmoidal shape, normally an “S”shape. In an embodiment, the links are configured to provide bothexpansion and contraction between adjacent unit segments.

In an embodiment, a double curvature link includes two curved portionsand a straight portion therebetween. In one embodiment, the connectinglinks within the same connecting link column are oriented in the samedirection, the direction being generally different than the direction ofan adjacent connecting link column.

In an embodiment, at least some, usually all of the straight portions oflinks within the same column form an oblique angle, normally either anacute or an obtuse angle with an imaginary longitudinal axis of theprosthesis. In one embodiment, at least some, usually all, of thestraight portions of the connecting links of an adjacent column areinclined at a supplementary angle, with the longitudinal axis of theprosthesis, to that of its adjacent connecting column. Supplementaryangle, as used herein, refers to two or more angles which together forma 180 degree angle with an axis.

The use of such sigmoidal links is beneficial since it permits thelongitudinal expansion or contraction of the prosthesis to accommodatelength changes as the prosthesis is expanded. Such links further permitbending of the prosthesis since they allow differential motion ofadjacent serpentine rings. Such flexibility is particularly advantageoussince it allows improved tracking of the prosthesis as it is deliveredto an endoluminal location. The sigmoidal links also improve theconformability of the expanded prosthesis when placed in a nativevessel, artificial graft, or other body lumen location. In theembodiments where the links attach away from the apex of the hingeregion, stress at the apex is reduced and uniform expansion of each ringsegment is enhanced.

The dimensions of the luminal prosthesis will depend on its intendeduse. Typically, the prosthesis will have a length in the range fromabout 1 to 100 mm, usually being from about 8 to 50 mm for vascularapplications; and from about 20 to about 200 mm, usually being fromabout 50 to about 150 mm for non-vascular applications.

The small (radially collapsed) diameter of the cylindrical prostheseswill typically be in the range from about 0.25 to about 20 mm, usuallybeing from about 0.4 to about 15 mm, and normally from about 0.8 toabout 10 mm.

The small (radially collapsed) diameter of cylindrical prostheses forvascular applications typically range from about 0.25 to about 1.5 mmfor coronary and from about 1 to about 4 mm for peripheral applications,usually from about 0.4 to about 1.25 mm for coronary and from about 1.5to about 3 mm for peripheral applications, and normally from about 0.8to about 1.2 mm for coronary and from about 1.75 to about 2.5 mm forperipheral applications.

For nonvascular applications, the prosthesis will typically have a smalldiameter ranging from about 1.5 to about 20 mm, usually from about 2 toabout 15 mm, and normally from about 5 mm to about 10 mm.

The large (radially enlarged) diameter of the cylindrical prostheseswill typically be in the range from about 1 mm to about 100 mm, usuallybeing from about 1.5 mm to about 75 mm, and normally from about 2 toabout 50 mm.

The large (radially enlarged) diameter of cylindrical prostheses forvascular applications typically range from about 1 mm to about 7 mm forcoronary and from about 1 mm to about 30 mm for peripheral applications,usually from about 1.5 mm to about 5 mm for coronary and from about 3 mmto about 25 mm for peripheral applications, and normally from about 2 mmto about 4 mm for coronary and from about 5 mm to about 20 mm forperipheral applications.

For nonvascular applications, the prosthesis will typically have alarger diameter ranging from about 1 mm to about 100 mm, usually fromabout 5 mm to about 75 mm, and normally from about 10 mm to about 50 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an exemplary prosthesisembodying features of the present invention in unexpandedconfigurations.

FIGS. 2A and 2B are “rolled out” views of an exemplary embodiment of theprosthesis of FIG. 1.

FIGS. 2C and 2D are “rolled out” views of an exemplary embodiment of theprosthesis of FIG. 1, in unexpanded and expanded configurations,respectively.

FIG. 3 is a partial “rolled out” view of structure of FIG. 2A with thestraight portion of the links forming oblique angles with a longitudinalaxis of the prosthesis.

FIG. 4A is a partial “rolled out” view of an embodiment of the structurein FIG. 2A showing a straight portion of the hinge portions intersectingthe imaginary lines bisecting the curved portions of the links.

FIG. 4B is a partial “rolled out” view of an embodiment of the structurein FIG. 2A showing a straight portion of the hinge portions beingparallel to imaginary bisecting the curved portions of the links.

FIG. 5A is a partial “rolled out” view of an alternate embodiment of thestructure of FIG. 2A with the links emerging from the apices.

FIG. 5B is a partial “rolled out” view of an alternate embodiment of thestructure of FIG. 3 with the hinge regions of the longitudinallyadjacent rings being radially aligned with one another.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a radially expansible luminal prosthesis 10, such asa stent, generally embodying features of the present invention, andincluding a frame 13 formed from a plurality of radially expansible ringsegments 16. Although the final shape of the prosthesis 10 willgenerally be cylindrical, it should be appreciated that the prosthesismay also be conformable to non-cylindrical cross-sectional lumens andmay also be conformable to transversely curved lumens.

An exemplary luminal prosthesis 10 particularly intended forimplantation in the vasculature (e.g., coronary or peripheral) comprisesfrom 4 to 50 ring segments 16 (with 7 being illustrated), the segmentsbeing joined to a longitudinally set apart adjacent ring segment by atleast one link, such as sigmoidal link 19.

Now referring to FIGS. 2A through 2D, the ring segments 16, comprise aplurality of struts 22, normally linear struts, joined by hinge regions25. As shown, the hinge regions 25 have a curved shape and include anapex portion 28 with side potions 31 extending on either side of theapex and transforming into the strut 22, and trough region 34 oppositethe apex 28.

The links 19, connect proximate hinge regions, such as 25A and 25B, ofadjacent rings, such as 16A and 16B. The links connecting adjacent ringsegments, as for example 16A and 16B, form a radial column 37. Theconnecting links 19 generally have a smooth, multi (usually double)curvature shape, usually in a sigmoidal shape, normally an “S” shape.

The links 19 extend from some of the radial hinge regions within thesame ring segment 16, such that not all hinge regions of a ring segmentare connected to hinge regions of an adjacent ring, although embodimentsconnecting all of the proximate hinge regions, or other configurations,are within the scope of the present invention. By way of example, asshown in FIG. 2A, ring segment 16A and 16B, comprise hinge regions 25Aand 25B which are connected to one another by way of link 19, and hingeregions 25C and 25D, which are free from connections to a hinge regionon an adjacent ring. The connected hinge regions may alternate withnon-connected hinge regions or may have certain repeat patterns. Asshown in FIG. 2C, the connected and non-connected hinge regionsalternate in the mid-section of the prosthesis with the most distal twolink columns at both ends of the prosthesis emerging in a pattern of 3connected hinge regions followed by a non-connected hinge region.

Now referring back to FIG. 2A and its enlarged view FIG. 2B, the doublecurvature links 19 include two curved portions, 40, such as 40′ and 40″,and a straight portion 43 disposed therebetween. The connecting links 19within the same connecting link column 37 are oriented in the samedirection with the straight portion 43 of at least some of the linksform an oblique angle with an imaginary longitudinal axis 46 of theframe 13.

By way of example, the straight portion of the links of two adjacentcolumns may form similar type of angles with the longitudinal axis,e.g., obtuse or acute. Furthermore, the angles within the same column,even when generally either obtuse or acute, may be similar or differentthan another angle within the same column.

As further shown in FIG. 3, the straight portion 43A of the connectinglinks 19A in one column 37A forms an obtuse angle α with the imaginarylongitudinal axis 46 of the frame 13. The obtuse angle α within eachcolumn, independently, ranges from about 95 to about 170, usually fromabout 100 to about 135, and normally from about 105 to about 130degrees.

The straight portion 43B of the connecting links 19B of a column 37Badjacent to column 37A, forms an acute, angle β with the longitudinalaxis 46. The acute angle β within each column, independently, rangesfrom about 10 to about 85, usually from about 45 to about 80 andnormally from about 50 to about 75 degrees.

The obtuse and acute angles, α and β, of adjacent rings, preferably,together, form supplementary angles with the longitudinal axis 46.

In one embodiment, links 19 have similar dimensions (e.g., the length ofthe straight portion 43A is similar, usually the same, as the length ofthe straight portion 43B) such that links in adjacent columns are mirrorimages one another.

Although the prosthesis as shown includes an even number of connectingcolumns 37 with the straight portion of the alternating columns formingeither obtuse or acute angles, the invention is not limited to suchalternating pattern and other configurations and patterns are within thescope of the present invention.

As can be seen in FIG. 4A, in one embodiment, curved portions 40′A and40″A of the multi-curvature link 19, project in opposite directions suchthat an imaginary axis 46A of the straight portion 43A, at each endintersects one imaginary line which bisects one of the curved portions.As shown, imaginary lines 49′A and 49″A, each bisects the curvedportions, 40′A and 40″A, respectively. The intersection of the axis 46″Aof the straight portion with imaginary lines 49′A and 49″A,respectively, forms angles λ and μ, respectively. It should beappreciated that although the intersection of the bisecting lines withthe imaginary axis of the straight portion has been described withrespect to one link column such as one forming obtuse angle with thelongitudinal axis of the prosthesis, intersections may also be formed inadjacent columns which form acute angles with the longitudinal axis ofthe prosthesis.

As further can be seen in FIG. 4B, in one embodiment, imaginary lines59′A and 59″A bisecting the curved portions 62′A and 62″A, respectively,of a link 65A, are parallel with the axis 68A of the straight portion71A.

In one embodiment, features of which are also shown in FIG. 4B, there isat least one radial plane 74 that intersects both curved portions, 77′and 77″, of a given link, 78. It should be appreciated that this featuremay be present independent of the other features previously discussedwith reference to FIGS. 4A and 4B.

Now referring to FIG. 5A, in an alternate embodiment, the links 74generally emerge from apex portion 77 of hinge region 80, as compared tothe side portions described earlier in reference to FIG. 2.

In one alternate embodiment, features of which are shown in FIG. 5B, theconnected hinge regions, such as hinge regions 83A and 83B are radiallyaligned with one another, as compared to the radially offset hingeregions in FIG. 2.

In operation, the prosthesis of the present invention, may be placed onan expandable portion of a balloon catheter, or within the lumen of adelivery catheter, and delivered to a desired luminal site and disposedtherein, as is known in the art.

Although certain preferred embodiments and methods have been disclosedherein, it will be apparent from the foregoing disclosure to thoseskilled in the art that variations and modifications of such embodimentsand methods may be made without departing from the true spirit and scopeof the invention. Therefore, the above description should not be takenas limiting the scope of the invention which is defined by the appendedclaims.

1. A radially expansible luminal prosthesis comprising: a plurality ofserpentine ring segments including struts and hinge regions disposedtherebetween; multi-curvature links including two curved portions and atleast one straight portion disposed therebetween which forms an obliqueangle with an imaginary longitudinal axis of the prosthesis, the linksconnecting at least some of the hinge regions on adjacent serpentinerings, wherein the links connecting immediate adjacent rings form aradial column with the straight portion of all of the links of the sameradial column either forming an acute or obtuse angle with thelongitudinal axis of the prosthesis, and wherein for all of the links ofthe same radial column there is at least one imaginary radial plane thatintersects all of the curved portions.
 2. The prosthesis of claim 1wherein all the angles of the same radial column are substantiallysimilar.
 3. The prosthesis of claim 2, wherein the angle of one radialcolumn is supplementary to the angle of an adjacent radial column. 4.The prosthesis of claim 2, wherein the radial links of adjacent radialcolumns are mirror images of one another.
 5. The prosthesis of claim 1,wherein the multi-curvature link includes two curved portions projectingin opposite directions from one another with the straight portiondisposed therebetween, with an imaginary axis of the straight portion ateach end forming an imaginary angle with one imaginary line bisectingone of the curved portions.
 6. The prosthesis of claim 1, wherein themulti-curvature link includes two curved portions with the straightportion disposed therebetween, with the curved portions projecting inopposite direction such that an imaginary axis of the straight portionat each end forms an imaginary angle with one imaginary line bisectingone of the curved portions.
 7. The prosthesis of claim 6 wherein theangles formed by each of the bisecting lines are substantially similarin value.